Abstract: Swirl atomizer inner core is the most important swirling component of the pressure swirling atomizer, the geometric topology of the swirl atomizer inner core directly affects the spray characteristics of pressure swirling atomizer.The current smooth acceleration section of the swirl atomizer inner core has lower flow efficiency.In order to reduce the energy loss, the swirl atomizer core accelerating section with ladder type has been designed to make spray medium pre-swirl and enhance the swirl strength in this paper, the lower part rotates 15° relative to the upper part, and the direction of the rotation is the same as the direction of the swirling slots of the atomizer. Spray flow rate, spray Sauter mean diameter(SMD), spray cone angle and droplet velocity were experimentally investigated by making use of particle dynamics analysis system(PDA) and charge coupled device experimental system(CCD) before and after the structure improvement of the acceleration section, and the axial and radial distributions of SMD and droplet velocity were also analyzed. Under the pressure ranges from 0.08 MPa to 0.46 MPa, the ladder type acceleration section has the better pre-swirl effect. The flow characteristics of the atomizer were increased by 48% to 51.8%; the axial and radial velocity of the spray were increased by 31.4% to 32.8% and 1.6% to 16.8%, respectively.The spray cone angle was reduced by 4.21° to 6.57°, and the SMD at downstream of the spray was decreased by 9.2% under higher pressure conditions.Compared with the smooth accelerating section, the application of ladder type accelerating section is beneficial to improve the quality of atomization.